The use of a home television set has grown dramatically in recent years. Not only does it display real life images in full color and motion, but the current popularity of interactive video games and personal computers has created a large demand for computer generated images having color and motion also. These computer generated images are "built" from a large number of picture elements (pixels) having various colors. They are stored as binary digits in a so-called "video memory" and periodically retrieved from memory to refresh a picture on the television set.
In a two-dimensional visual display apparatus, such as a television set, it is desirable to create the effect of a third dimension whereby various images exist in different planes. The problem is made more complex when individual images are animated or otherwise required to move in front of some images yet behind others. In the prior art there are disclosed a number of methods for overlaying video images to thereby generate a three-dimensional effect.
One such method is disclosed in U.S. Pat. No. 4,317,114 issued on Feb. 23, 1982 to J. T. Walker. In this patent there is disclosed a plurality (n) of memories for superpositioning images over a host image. There are as many individual video memories as there are image planes, and pixels are given priority according to the particular video memory in which they are stored. Priortization according to storage location is thus the vehicle for determining which image will overlay a competing image. Such a system minimizes the processing complexity associated with priortization while increasing the required hardware.
Another method for providing various image planes stores all pixels within a single memory; however when it is desired to display one or more objects in motion, the processing complexity and real-time consumption increases substantially.
It is therefore an object of the present invention to provide a video display technique in which images can be displayed in various planes and thereby portray depth in such displays.
It is another object of the present invention to modify the content and number of image planes without modification to the stored image data or to the hardware configuration.
It is yet another object of the invention to minimize the number of video memories required to generate the various image planes.